1. Field of the Invention
The present invention relates to a system for retrieving multimedia data and a method thereof, in particular to a content-based multimedia retrieval system and a method thereof which is capable of retrieving multimedia data among different systems using color histograms constructed with different color spaces and color quantization methods.
2. Description of the Prior Art
In retrieval of content-based multimedia data in the conventional technology, color distribution of an image is displayed as a color histogram, the color histogram is defined in accordance with a color space and a color quantization method.
In addition, in retrieval of content-based multimedia data in the conventional technology, the color histogram is mainly used.
In other words, it is possible to perform an image or a video retrieval based on colors among systems using color histograms constructed with same color spaces and quantization methods on the internet circumstances. On the contrary, it is impossible to perform the image or video retrieval among systems using color histograms constructed with different color spaces and different quantization methods each other.
Herein, the color histogram displays the color distribution of the image, is easy to calculate similarity for comparing the color histograms, has a character unconcerned in position of a color pixel (Sometimes, a character concerned in position of a color pixel is needed in an image retrieval. For that, other feature display is used.), and has a better performance than the other color display method (texture histogram) for content-based image retrieval.
The content-based multimedia retrieval system using the color histogram will now be described with reference to accompanying FIG. 1.
FIG. 1 is a block diagram illustrating the construction of the content-based multimedia retrieval system using color histograms in accordance with the conventional technology.
As depicted in FIG. 1, the content-based multimedia retrieval system using the color histogram comprises a color quantizer 100 for being inputted query image inputted by a user and extracting a color histogram as feature information of the query image, an image database 103 for storing a plurality of retrieval object image data 103-1˜103-N, a feature database 102 for storing the color histograms 102-1˜102-N as the feature information of the plurality of retrieval object images, and a retrieval unit 101 for calculating similarity between the color histogram of the query image and the color histograms of the plurality of retrieval object images and outputting an image in accordance with the similarity as a retrieval result.
The operation of the content-based multimedia retrieval system using the color histogram in accordance with the conventional technology will now be described.
First, the color quantizer 100 extracts the color histograms 102-1˜102-N in order to find the feature information of the image data 103-1˜103-N about the plurality of retrieval object images. In other words, the color quantizer 100 extracts one color histogram 102-1 per each image 103-1.
The extracted color histograms 102-1˜102-N are connected to the pertinent images 103-1˜103-N, and are stored on the feature database 102. In other words, the extracted color histograms 102-1˜102-N stored on the feature database 102 display the color distribution of the each image.
In addition, when the query image is inputted by the user, the color quantizer 100 extracts the color histogram about the query image.
In other words, the color quantizer 100 quantizes the designated color space into a plurality of subordinate spaces in accordance with the designated color space and quantization method.
Herein, the each quantized subordinate space is matched to one bin, color values of all pixels in a certain image constructs a color histogram in proportion to a frequency of occurrence corresponding to the each subordinate space.
The retrieval unit 101 calculates the similarity of the color histograms 102-1˜102-N displaying the color histogram of the extracted query image and the color distribution of the retrieval object images 103˜103-N stored in the feature database 102, and outputs the retrieval result in accordance with the similarity.
For example, the retrieval unit 101 calculates the similarity of the histograms 102-1˜102-N extracted in advance for the image retrieval based on the color and stored in the feature database 102 and the histogram of the query image by using a known method, namely, a histogram matching method such as a histogram intersection, and outputs the each image corresponding to the color histogram as a retrieval result on the basis of the magnitude of the calculated similarity value.
Herein, when the color histogram of the query image is extracted in advance and is stored in the feature database 102, the retrieval unit 101 calculates the similarity between the color histogram of the query image extracted in advance and the color histograms of the retrieval object images, and outputs an image in accordance with the similarity as a retrieval result (There is no need to extract newly the color histogram of the query image by the color quantizer.).
On the contrary, when the query image is not stored on the feature database 102 after being extracted in advance, the color quantizer 100 extracts newly the color histogram of the query image, and provides it to the retrieval unit 101.
However, in the conventional content-based multimedia retrieval system using the color histogram, it is possible to compare the color histograms among different systems only when the same color space and same color quantization are adapted to the color quantizers.
For example, when the color histograms constructed with same color space and same quantization method are used between same two systems on the internet circumstances, it is possible to perform the multimedia data retrieval based on the colors.
On the contrary, between two different systems, when color histograms constructed with color spaces and quantization method are not same, it is impossible to perform the multimedia data retrieval based on the colors. It will now be described with reference to accompanying FIG. 2.
FIG. 2 illustrates multimedia retrieval relations between different systems in accordance with the conventional technology.
As depicted in FIG. 2, because the meaning of each bin of the color histogram is changed by different color space and different color quantization, comparing a color histogram used in a local system A 200 with a color histogram used in a local system B is impossible.
For example, when color histograms 201-1˜201-N of images are stored in the feature database 201 of the local system A 200, a color histogram having 125 (5×5×5) bin number is constructed by performing 5 levels of uniform quantization about each RGB element by using a RGB (Red Green Blue) color space 202.
When color histograms 205-1˜205-N of images are stored on the feature database 205, the local system B 204 constructs and stores a color histogram having 343 (7×7×7) bin number by performing 7 levels of uniform quantization about each HSV (Hue Saturation Value) element by using a HSV (Hue Saturation Value) color space 206.
Accordingly, it is impossible to compare the color histogram of the local system A with the color system of the local system B.
As described above, in the conventional technology, it is impossible to perform the multimedia data retrieval between the systems using the color histograms constructed with the different color spaces and color quantization methods each other.
In addition, in the conventional technology, it is impossible to retrieve a retrieval object image about a query image of itself in a database of the other party between the systems using the color histograms constructed with the different color spaces and color quantization methods.
In addition, in the conventional technology, it is impossible to connect the databases which store various, different, wide range of images to a retrieval unit in a network circumstances such as the internet in order to retrieve images.